The need for, and desirability of, a blood substitute has become increasingly clear over the last several years. Not only is there a shortage of whole blood available for transfusions, for a variety of reasons, but there is the fear, both real and imagined, of the transmission of communicable diseases through the use of whole blood transfusions. Such diseases include, for example, hepatitis and AIDS.
Still further, there are emergency situations in which whole blood, even if otherwise available, is not present for use. For example, ambulances generally do not have the necessary storage facilities for whole blood. Persons in remote locations, who may require transfusions, including those in space flight, do not have access to banks of whole blood.
In a typical year, ten million units of whole blood are collected for use in transfusions. Of these, approximately 53% are transfused as whole blood. The red blood cells are removed from approximately 15% more of the blood obtained, and these are transfused in the form of the cells. However, whole blood has a finite storage life, even when adequately stored, and approximately 25% of the whole blood collected in any year must be discarded.
While the hemoglobin from this blood to be discarded could be saved, early attempts at using it failed, when fragments of red blood cells, referred to as stroma, were found to clog small blood vessels and cause blockages. Recently, however, filtration processes have been developed to produce a stroma-free hemoglobin.
Since no oxygen transport and transmission system equivalent to hemoglobin has ever been discovered, scientists have long sought means of employing the hemoglobin which is otherwise discarded, even the stroma-free hemoglobin. Efforts in the past have, however, proven unsuccessful.